I am very confused about RBb crossover schematic...

[SanJoseMichael]

I am very confused about this crossover schematic from Infinty RSb speakers. While redoing the crossovers, this was not making sense to me, though I do admit to being relatively new at this. Schematic below.

Tweeter (Blue highlight) makes sense, positive in, positive out.

Midrange (Yellow highlight) negative in to positive out? Huh?

Woofer (Green highligh) postive in to negative out? What?

Does this mean the midrange and woofer are out of phase with the tweeter?

 

[geoff727]

On the schematic, where there's a dot, that's where the connection is. Where lines cross (like your yellow/green lines), that means that those wires don't connect. So, on the woofer, this means that the - post of the woofer is connected to the + binding post. The - binding post should trace from the post, through the 2.5mH inductor, past a connection for the 100uf shunt cap, and on to the woofer's + connector. On the midrange, the + binding post should lead to numerous connections for the crossover components, through the variable resistor (the adjustable 5-ohm pot), then to the - connector of the midrange. In other words, the midrange and woofer are wired out of phase with the tweeter.

Don't think too much of it. In 2nd order crossover networks, it is very common for one driver to be wired out of phase with another. This stems from how the phase of the audio signal rotates around when the combination of caps and inductors introduce their electrical phase shifts. As always, verify the schematic against what's actually inside the speaker. If the speaker is wired differently than the schematic (i.e., with a different combination of, or all the drivers in phase), you can do one of two things: leave the wiring inside the speaker as-is, or change the wiring to match the schematic. Not all these schematics are 100% accurate; a lot of these speakers went through different iterations and making schematics for each one would be really tough and a huge amount of research on things that are now 30 and 40 years old. If you decide to change + and - connections, let your ears be the final judge. Whatever sounds best to you is correct. You won't hurt anything by reversing polarity on any of the drivers. It will just change how the signals sum acoustically, and therefore affect the final sound.
G~

 

[SanJoseMichael]

"In other words, the midrange and woofer are wired out of phase with the tweeter."

Big thanks for the time you spent on the reply. I have only recently come to realize that over a production run of anything electrical, component changes happen when stocks run low on one part, and another part can be had for 23 cents cheaper. Production keeps running, and let the engineering and support guys publish whatever schematic is available from documentation.

The crossovers on the speakers as I got them did not match, so I found a pair that did match on CheeseBay. Those matched each other but not the schematic. I chose to leave the wiring as is on the new matching xo's, replacing caps one at a time (I have learned never to replace more than one thing at once on my workbench at my skill level. My Scott 222C survived, as did my Magnavox 175 and 8802 per that rule).

What I did do was to wire the RSb's in reverse at the binding posts, as it lines up psychologically with polarization per the schematic. I know that it can't matter (unless one speaker is out of phase with the other, phase cancellation, etc) so black black red red is the same as black red black red. My ears are happy (except for speaker/amp love or indifference).

Thanks again, Audiokarma, for all the great advice over the many years and solder burned fingers.

MG

 

[I LIKE MUSIC]

This topic can be confusing to those trying to learn about it when polarity and phase are equated.

They are not the same thing.

In the schematic posted, the polarity of the midrange driver is reversed. This has no impact on the time domain relationships (phase/group delay).

 

[SanJoseMichael]

Time domain or delay? As in DCM, Bowers&Wilkins, Vandersteen, or Altec driver physical alignment?? I am nearly over my head here...

 

[I LIKE MUSIC]

In general, delay happens in the time domain.

In simple terms...

If we are speaking about the relationship of signals of the same frequency we can talk about their phase relationship (still a difference in time). If we are talking about a range (group) of frequencies then we talk about group delay (again a difference in time). In the nitty-gritty of engineering it is somewhat more involved, but this example works for a simple example.

The relationship in the time domain between the signals can happen electronically within the crossover circuitry or physically by the position of the speaker drivers or a combination of both.

 

[rogerr1]

I re-foamed my RSb woofers and in the process sketched the crossover schematic and measured all the values except for the pots. Many differences compared to Infinity's Rev A crossover. For now, I shorted out the pots. At some point I may substitute nominal resistors. I never found the pots very useful, more annoying than anything. I drive the RSb's with a Hafler DH-200. I bought the speaks new in around 1902. Oops, 1982.
Referencing my sketch, here are the values I measured at 1kHz with my Insight U1733C:

9104673 9104677
C1 = 7.55uF, D=0.028, phase -88.3 C1 = 7.53uF, D=0.024, phase -88.6
C2 = 15.1uF, D=0.042, phase -87.5 C2 = 15.4uF, D=0.050, phase -87.1
C3 = 12.8uF, D=0.044, phase -87.4 C3 = 13.3uF, D=0.053, phase -86.9
C4 = 132uF, D=0.044, phase -87.4 C4 = 135uF, D=0.042, phase -87.5
L1 = 0.102mH, Q=5.32, phase 79.3 L1 = 0.109mH, Q=5.28, phase 79.2
L2 = 2.0mH, Q=12.2, phase 85.3 L2 = 2.0mH, Q=12.1, phase 85.2
L3 = 0.598mH, Q=7.91, phase 82.7 L3 = 0.586mH, Q=7.77, phase 82.6
L4 = 1.2mH, Q=8.94, phase 83.5 L4 = 1.38mH, Q=8.02, phase 82.8

(I pulled all the silly staples so I could easily disconnect the components for measuring. Now I have 7 screws holding each one in place.)

 

[rogerr1]

My formatting is a bit messy but basically I've listed each part by speaker serial number. So just image that 9104677 is tabbed over so it's above the other C1.

 

[rogerr1]

FWIW, after listening a bit, I decided that shorting the pots out wasn't to my satisfaction. As someone said in another RSb discussion, shorting the pots makes the speaker a bit too "forward" sounding. I installed a 2 ohm / 25W wirewound for the mid and a 2.2 ohm / 5W for the tweeter. Happy with that.

I wasn't totally clear in my previous posts but the Rev A crossover schematic, that's readily available online (shown in the first post above), is NOTHING like what came in my speakers. What I have actually makes sense...input minus goes to speaker minus for all 3 drivers, etc.